A 7514-Da chymotrypsin inhibitor was isolated from the seed extract of Momordica cochinchinensis (Family Cucurbitaceae) by chromatography on chymotrypsin Sepharose 4B and subsequently by C18 reversed-phase HPLC. This inhibitor, named MCoCI, possessed remarkable thermostability and was stable from pH 2 to 12. MCoCI also inhibited subtilisin, but had at least 50-fold lower inhibitory activity towards trypsin and elastase. Amino acid sequencing of a peptide fragment of MCoCI revealed a sequence of 23 amino acids. Comparison of this sequence and the molecular mass with those of other protease inhibitors suggests that MCoCI belongs to the potato I inhibitor family.
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